There are SO MANY reviews of various K-girls here - you are asking such an easy and obvious answer, you should expect to receive some flack for your laziness!!!
Why don't you get off your ass and do a search for "korean" or "K-girl" here first, do your own research first, and if you have further questions than ask it. You are asking such an open-ended question, the answers you get from us won't be too useful anyways.
Its a bit of a harsh response, I know, but you'd be surprised about the number of newbies asking simple questions that just clog everything up. If we took the time to spoon feed each and every one of them they'd never grow up.
I'll throw you a bone. 5890, richmond penthouse, and outlook are some of the more reputable agencies. Its only at the Penthouse which you will need to sit in a living room with a random punter awaiting your turn, while some other john is drilling through the girl you booked and are next in line for.